A fuel cell is an electrochemical device that produces electrical current from chemical reactions. The fundamental device includes an ion-conducting electrolyte between two electrodes, backed by fuel and oxidant flow distributors. A catalyst on one electrode promotes separation of ions and electrons at the oxidant side. Only the ions conduct through the electrolyte, and recombine with electrons at the fuel side. The electrons are conducted through an external circuit, thus supplying electrical power. Solid oxide fuel cells (SOFC's) have ionic-conducting metal oxide membranes as their electrolyte layer. The oxygen molecules are split into their respective electrons and oxygen ions at the airside. The oxygen ions propagate through the electrolyte membrane and combine with their electrons and hydrogen molecules into water. A gas sensor has the same basic configuration, and produces electrical current that depends on difference of gas concentration.
Fuel cell operation is increasingly efficient where the well-known electron conductivity of the electrolyte is brought to a minimum and the well-known ionic conductivity of the electrolyte is brought to a maximum. At the same time it is well known that a fuel cell is thermodynamically more efficient at lower temperatures, with lower entropic losses resulting in a higher open cell voltage.
Solid oxide fuel cells [SOFC] have a number of advantages:                No humidity requirement for ion exchange        No water clogging up with generated water        No or less noble metal catalyst        High CO tolerance        Valuable waste heat        
However, SOFCs have problems. One of the main problems to be overcome is preparation of hermetic seals. With decreasing operating temperature from 1000° C. to 600° C. or less, metal materials can be used for sealing and the problem becomes manageable. Many efforts have been made to decrease operating temperature of SOFCs to below 600° C. despite a large loss of output power. However, this operating temperature is still too high for mobile application.
In particular, an electrolyte layer is needed that may be fabricated in an inexpensive fashion with a configuration that provides for an efficient fuel cell operation at working temperatures of generally less than 500° C. The present invention addresses also these needs.